1. Field of the Invention
The present invention relates to a flexible circuit board.
2. Description of the Related Art
A resin composition of, e.g., polyimide (PI), polyethylene terephthalate (PET), or polyethylene naphthalate (PEN) is generally used as the material for a base film of a flexible circuit board (FPC) (see Patent Documents 1 and 2). For example, Patent Document 2 discloses a configuration which uses polyimide or polyethylene terephthalate as the material for a base film of a flexible circuit board.
However, a configuration using a film of a resin composition as a base film of a flexible circuit board may suffer from the problems below.
Resin compositions as described above are expensive, which makes it difficult to reduce the price of a flexible circuit board.
Examples of a flexible circuit board include a carrier tape for TAB (Tape Automated Bonding). A carrier tape for TAB has a sprocket hole for positioning in bonding and a device hole for mounting a device, an electronic component, or the like. A sprocket hole and a device hole are openings extending through a base film in a thickness direction. Etching or die-punching is used to form such an opening. A process of forming an opening in a base film of a resin composition by etching is costly and is very low in processing rate. Die-punching requires facilities for punching, which increases facilities cost.
Flexible circuit boards have been increasing in width in order to, e.g., enhance production efficiency. However, a base film made of a resin composition is considerably deformed or varies widely in dimensions due to a temperature change, moisture absorption, or the like. For this reason, the yield of flexible circuit boards using a resin composition as the material for a base film tends to decrease with an increase in width.
In recent years, the density or the number of layers of wiring patterns to be formed at a flexible circuit board or devices or the like to be mounted on the flexible circuit board has been increasing. However, due to the low thermal conductivity of a resin composition, the higher density or the larger number of layers increases thermal load on a mounted device and the like. An increase in the density or the number of layers is thus hard to achieve.
Patent Document 1
    Japanese Laid-open Patent Publication No. 05-029395Patent Document 2    Japanese Laid-open Patent Publication No. 2007-18926